Upsert Bulk vs Batch Upsert in Salesforce

Question

I'm attempting to import a significant amount of information into Salesforce. This can be done in two ways, according to my research. 1. Make use of UpsertBulk. This will upsert data all at once. 2. Make use of batching Make an upsert job. For the upsert process, create batches.

What is the distinction between these two approaches? What is the most effective approach to bulk upsert?